Composite soft magnetic sintered material having high density and high magnetic permeability and method for preparation thereof

ABSTRACT

An object of the present invention is to provide a composite soft magnetic sintered material that has high density, high mechanical strength and high relative magnetic permeability at high frequencies and, in order to achieve this object, the present invention provides a method of producing the composite soft magnetic sintered material, which comprises mixing a composite soft magnetic powder, that consists of iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or nickel-based soft magnetic alloy powder (hereinafter these powders are referred to as soft magnetic metal powder) of which particles arc coated with a ferrite layer which has a spinel structure, with 0.05 to 1.0% by weight of silicon dioxide powder having a mean powder particle size of 100 nm or less and sintering the mixed powder after compression molding, or processing two or more kinds of the composite soft magnetic powders, of which particles are coated with ferrite layer having a spinel structure of a different compositions, by compression molding and sintering.

TECHNICAL FIELD

The present invention relates to a composite soft magnetic sinteredmaterial having high density and high magnetic permeability, and amethod of producing the same.

BACKGROUND ART

Soft magnetic sintered materials are used in magnetic cores for suchdevices as low-loss yoke, transformer and choke coil used in motors,actuators or the like. And it is known that the soft magnetic sinteredmaterials can be obtained by sintering a soft magnetic metal powder suchas:

-   -   iron powder such as pure iron powder;    -   Fe—Si based soft magnetic iron alloy powder containing 0.1 to        10% by weight of Si with the rest consisting of Fe and        inevitable impurities (for example, iron alloy powder of Fe-3%        Si);    -   Fe—Si—Al based soft magnetic iron alloy powder containing 0.1 to        10% by weight of Si and 0.1 to 20% by weight of Al with the rest        consisting of Fe and inevitable impurities (for example, Sendust        iron alloy powder having a composition of Fe-9% Si-5% Al);    -   Fe—Al based soft magnetic iron alloy powder containing 0.1 to        20% by weight of Al with the rest consisting of Fe and        inevitable impurities (for example, Alperm iron alloy powder        having a composition of Fe-15% Al);    -   Fe—Cr based soft magnetic iron alloy powder containing 1 to 20%        by weight of Cr and, as required, one or two of 5% or less Al        and 5% or less Si with the rest consisting of Fe and inevitable        impurities; or    -   nickel-based soft magnetic alloy powder containing 35 to 85% of        Ni and, as required, one or more of 5% or less Mo, 5% or less        Cu, 2% or less Cr and 0.5% or less Mn with the rest consisting        of Fe and inevitable impurities (for example, powder of Fe-79%        Ni) (hereinabove percentages are by weight). It is also known        that soft magnetic sintered materials can be obtained by        sintering a powder of a metal oxide such as ferrite that has a        spinel structure. The ferrite having a spinel structure is        generally represented by formula (MeFe)₃O₄ (where Me represents        Mn, Zn, Ni, Mg, Cu, Fe or Co, or a mixture of some of these        elements).

However, although the soft magnetic sintered metals have high saturationmagnetic flux densities, they are inferior in high frequencycharacteristics. The soft magnetic sintered metal oxides that are madeby sintering powder of a metal oxide such as ferrite having a spinelstructure, on the other hand, have good high frequency characteristicsand relatively high initial magnetic permeability, but have lowsaturation magnetic flux densities. In order to overcome thesedrawbacks, a composite soft magnetic sintered material has been proposedthat is obtained by sintering a composite soft magnetic powder formedfrom a soft magnetic metal powder of which particles are coated withlayers of ferrite having a spinel structure on the surface thereof(refer to Unexamined Japanese Patent Application, First Publication No.Sho 56-38402).

However, in the composite soft magnetic sintered material that isobtained by sintering the composite soft magnetic powder formed from thesoft magnetic metal powder of which particles are coated with layers offerrite having a spinel structure on the surface thereof, the ferritelayer having a spinel structure is made of an oxide and it is thereforedifficult to sinter, thus resulting in a problem that the composite softmagnetic sintered material that has a sufficient density cannot beobtained. Thus there is a demand for a composite soft magnetic sinteredmaterial having further improved magnetic characteristics.

DISCLOSURE OF THE INVENTION

The present inventors have intensively studied the problem describedabove and found the following:

-   (A) A mixed powder having improved sintering characteristics can be    obtained by preparing a composite soft magnetic powder by forming a    ferrite layer which has a spinel structure on the surfaces of    particles of iron powder, Fe—Si based soft magnetic iron alloy    powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based    soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron    alloy powder or nickel-based soft magnetic alloy powder, and mixing    the composite soft magnetic powder with 0.05 to 1.0% by weight of    silicon dioxide powder having a mean powder particle size of 100 nm    or less. A composite soft magnetic sintered material, that is made    from the mixed powder containing the silicon dioxide powder by    compression molding, high-pressure molding, warm compaction or cold    isostatic pressing followed by sintering, or by hot isostatic    pressing or hot pressing, has higher density and hence higher    mechanical strength, and has higher magnetic characteristics and,    particularly, improved relative magnetic permeability at high    frequencies;-   (B) A mixed powder, that is obtained by mixing two or wore kinds of    composite soft magnetic powders made by forming ferrite layer which    has a spinel structure of a different composition on the surfaces of    particles of iron powder, Fe—Si based soft magnetic iron alloy    powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based    soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron    alloy powder or nickel-based soft magnetic alloy powder, and    sintering the mixed powder after compression molding, high-pressure    molding, warm compaction or cold isostatic pressing, or processing    the mixed powder by hot isostatic pressing or hot pressing, is    easier to sinter than in such a case as the composite soft magnetic    powder coated with ferrite layer of the same type is processed by    compression molding, high-pressure molding, warm compaction or cold    isostatic pressing followed by sintering, or by hot isostatic    pressing or hot pressing. As a result, the composite soft magnetic    sintered material thus obtained has higher density and hence higher    mechanical strength, while the magnetic characteristics are improved    and, in particular, relative magnetic permeability at high    frequencies is improved;-   (C) A mixed powder, that is obtained by mixing two or more kinds of    composite soft magnetic powders made by forming ferrite layer of a    spinel structure that has a different composition on the surfaces of    particles of iron powder, Fe—Si based soft magnetic iron alloy    powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based    soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron    alloy powder or nickel-based soft magnetic alloy powder, with the    mixture being further mixed with 0.05 to 1.0% by weight of silicon    dioxide powder having a mean powder particle size of 100 nm or less,    has further improved sintering characteristics. A composite soft    magnetic sintered material, that is made from the mixed powder    containing silicon dioxide powder by compression molding,    high-pressure molding, warm compaction or cold isostatic pressing    followed by sintering, or by hot isostatic pressing or hot pressing,    has higher density and hence higher mechanical strength, while the    magnetic characteristics are improved further and, in particular,    the relative magnetic permeability at high frequencies is improved    further,-   (D) In the composite soft magnetic sintered material obtained by the    method (A) described above, the iron particles, Fe—Si based soft    magnetic iron alloy particles, Fe—Al based soft magnetic iron alloy    particles, Fe—Si—Al based soft magnetic iron alloy particles, Fe—Cr    based soft magnetic iron alloy particles or nickel-based soft    magnetic alloy particles that are coated with a ferrite phase having    a spinel structure on the surface thereof are dispersed and the    silicon dioxide powder having a mean powder particle size of 100 nm    or less that is added thereto does not form a solid solution with    the ferrite phase even when sintered and therefore remains dispersed    in the ferrite phase. As a result, the composite soft magnetic    sintered material has such a structure as the silicon dioxide    particles having a mean powder particle size of 100 nm or less are    dispersed in the ferrite phase, and the proportion of the silicon    dioxide particles dispersed in the ferrite phase is from 0.05 to    1.0% by weight, the same as that of the silicon dioxide powder that    was added;-   (E) The composite soft magnetic sintered material obtained by the    method (B) described above has such a structure as the iron    particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al    based soft magnetic iron alloy particles, Fe—Si—Al based soft    magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy    particles or nickel-based soft magnetic alloy particles that are    coated with a ferrite phase which has a spinel structure and has a    different composition formed on the surface thereof are dispersed;-   (F) The composite soft magnetic sintered material obtained by the    method (C) described above comprises the iron particles, Fe—Si based    soft magnetic iron alloy particles, Fe—Al based soft magnetic iron    alloy particles, Fe—Si—Al based soft magnetic iron alloy particles,    Fe—Cr based soft magnetic iron alloy particles or nickel-based soft    magnetic alloy particles that are coated with a ferrite phase which    has a spinel structure and has a different composition formed on the    surface thereof being dispersed therein, wherein the silicon dioxide    powder, having a mean powder particle size of 100 nm or less, that    has been added thereto does not form a solid solution with the a    ferrite phase even when sintered and therefore remains dispersed in    the ferrite phase of a different composition, and the composite soft    magnetic sintered material has such a structure as the silicon    dioxide particles having a wean powder particle size of 100 nm or    less are dispersed in the ferrite phase that has a different    composition, and the proportion of the silicon dioxide particles    dispersed in the ferrite phase of a different composition is from    0.05 to 1.0% by weight, the same as that of the silicon dioxide    powder that was added; and-   (G) The ferrite layer having a spinel structure formed on the    particles of the iron powder, Fe—Si based soft magnetic iron alloy    powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based    soft magnetic iron alloy powder, Fe—Cr based soft magnetic iron    alloy powder or nickel-based soft magnetic alloy powder can be    formed by a chemical plating process, high-speed impact agitation    coating process where the coating layer is formed mechanically by    high speed agitation, or binder coating process where the coating    layer is formed by bonding with resin.

The present invention has been completed on the basis of the findingsobtained from the research described above, and is characterized by thefollowing features:

-   (1) A composite soft magnetic sintered material having high density    and high magnetic permeability with such a structure as iron    particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al    based soft magnetic iron alloy particles, Fe—Si—Al based soft    magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy    particles or nickel-based soft magnetic alloy particles, coated with    a ferrite phase that has a spinel structure are dispersed, and    silicon dioxide particles having a mean powder particle size of 100    nm or less are dispersed in said ferrite phase, wherein the content    of silicon dioxide is from 0.05 to 1.0% by weight;-   (2) A composite soft magnetic sintered material having high density    and high magnetic permeability with such a structure as iron    particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al    based soft magnetic iron alloy particles, Fe—Si—Al based soft    magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy    particles or nickel-based soft magnetic alloy particles, coated with    a ferrite phase that has a spinel structure of a different    composition are dispersed;-   (3) A composite soft magnetic sintered material having high density    and high magnetic permeability with such a structure as iron    particles, Fe—Si based soft magnetic iron alloy particles, Fe—Al    based soft magnetic iron alloy particles, Fe—Si—Al based soft    magnetic iron alloy particles, Fe—Cr based soft magnetic iron alloy    particles or nickel-based soft magnetic alloy particles, coated with    a ferrite that has a spinel structure of a different composition are    dispersed, and silicon dioxide particles having a mean powder    particle size of 100 nm or less are dispersed among said ferrite    phase, wherein the content of silicon dioxide is from 0.05 to 1.0%    by weight;-   (4) A method of producing the composite soft magnetic sintered    material having high density and high magnetic permeability    described in (1), wherein the composite soft magnetic powder, that    is made by forming a ferrite layer that has a spinel structure on    the surfaces of particles of iron powder, Fe—Si based soft magnetic    iron alloy powder, Fe—Al based soft magnetic iron alloy powder,    Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based soft    magnetic iron alloy powder or nickel-based soft magnetic alloy    powder, is mixed with 0.05 to 1.0% by weight of silicon dioxide    powder having a mean powder particle size in a range from 1 to 100    nm, and the mixed powder is sintered after compression molding,    high-pressure molding, warm compaction or cold isostatic pressing;-   (5) A method of producing the composite soft magnetic sintered    material having high density and high magnetic permeability    described in (1), wherein the composite soft magnetic powder, that    is made by forming ferrite layer which has a spinel structure on the    surfaces of particles of iron powder, Fe—Si based soft magnetic iron    alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al    based soft magnetic iron alloy powder, Fe—Cr based soft magnetic    iron alloy powder or nickel-based soft magnetic alloy-powder, is    mixed with 0.05 to 1.0% by weight of silicon dioxide powder having a    mean powder particle size in a rage from 1 to 100 nm, and the mixed    powder is subjected to hot isostatic pressing or hot pressing;-   (6) A method of producing the composite soft magnetic sintered    material having high density and high magnetic permeability    described in (2), which comprises preparing two or more kinds of    composite soft magnetic powders that are made by forming ferrite    layer which has a spinel structure of a different composition on the    surfaces of particles of iron powder, Fe—Si based soft magnetic iron    alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al    based soft magnetic iron alloy powder, Fe—Cr based soft magnetic    iron alloy powder or nickel-based soft magnetic alloy powder, mixing    and sintering two or more kinds of composite soft magnetic powders    after compression molding, high-pressure molding, warm compaction or    cold isostatic pressing;-   (7) A method of producing the composite soft magnetic sintered    material having high density and high magnetic permeability    described in (2), which comprises preparing two or more kinds of    composite soft magnetic powders, that are made by forming ferrite    layer having a spinel structure of a different composition on the    surfaces of particles of iron powder, Fe—Si based soft magnetic iron    alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al    based soft magnetic iron alloy powder, Fe—Cr based soft magnetic    iron alloy powder or nickel-based soft magnetic alloy powder, mixing    two or more kinds of the composite soft magnetic powders, and    subjecting them to hot isostatic pressing or hot pressing;-   (8) A method of producing the composite soft magnetic sintered    material having high density and high magnetic permeability    described in (3), which comprises preparing two or more kinds of    composite soft magnetic powders, that are made by forming ferrite    layer having a spinel structure of a different composition on the    surfaces of particles of iron powder, Fe—Si based soft magnetic iron    alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al    based soft magnetic iron alloy powder, Fe—Cr based soft magnetic    iron alloy powder or nickel-based soft magnetic alloy powder, mixing    two or more kinds of the composite soft magnetic powders with 0.05    to 1.0% by weight of silicon dioxide powder having a mean powder    particle size in a range from 1 to 100 nm, sintering the mixed    powder after compression molding, high-pressure molding, warm    compaction or cold isostatic pressing;-   (9) A method of producing the composite soft magnetic sintered    material having high density and high magnetic permeability    described in (3), which comprises preparing two or more kinds of    composite soft magnetic powders, that are made by forming a ferrite    layer having a spinel structure of a different composition on the    surfaces of particles of iron powder, Fe—Si based soft magnetic iron    alloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al    based soft magnetic iron alloy powder, Fe—Cr based soft magnetic    iron alloy powder or nickel-based soft magnetic alloy powder, mixing    two or more kinds of the composite soft magnetic powders with 0.05    to 1.0% by weight of silicon dioxide powder having a mean powder    particle size in a range from 1 to 100 nm, and subjecting the mixed    powder to hot isostatic pressing or hot pressing; and-   (10) A method of producing the composite soft magnetic sintered    material having high density and high magnetic permeability    described in any one of (4), (5), (6), (7), (8) and (9), wherein the    composite soft magnetic powder, that is made by forming ferrite    layer having a spinel structure on the surface of the particles of    the iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Al    based soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic    iron alloy powder, Fe—Cr based soft magnetic iron alloy powder or    nickel-based soft magnetic alloy powder, is made by forming the    ferrite layer on the particles of the iron powder, Fe—Si based soft    magnetic iron alloy powder, Fe—Al based soft magnetic iron alloy    powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based    soft magnetic iron alloy powder or nickel-based soft magnetic alloy    powder by a chemical plating process, a high-speed impact agitation    coating process or a binder coating process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of a secondary electron image taken by an Augerspectrometer showing grain boundaries in sintered material No. 61 of thepresent invention.

FIG. 2 is a photograph of an Auger electron image of Si showing thedistribution of SiO₂ in the grain boundaries shown in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

The iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Albased soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic ironalloy powder, Fe—Cr based soft magnetic iron alloy powder ornickel-based soft magnetic alloy powder used in the method of producingthe composite soft magnetic sintered material of the present inventionhaving high density and high magnetic permeability is a soft magneticalloy powder that has been known to the public, for which the softmagnetic metal powder such as iron powder, Fe—Si based soft magneticiron alloy powder containing 0.1 to 10% by weight of Si with the restconsisting of Fe and inevitable impurities, Fe—Si—Al based soft magneticiron alloy powder containing 0.1 to 10% by weight of Si and 0.1 to 20%by weight of Al with the rest consisting of Fe and inevitableimpurities, Fe—Al based soft magnetic iron alloy powder containing 0.1to 20% by weight of Al with the rest consisting of Fe and inevitableimpurities, Fe—Cr based soft magnetic iron alloy powder containing 1 to20% by weight of Cr and, as required, one or two of 5% or less Al and 5%or less Si with the rest consisting of Fe and inevitable impurities; ornickel-based soft magnetic alloy powder containing 35 to 85% of Ni and,as required, one or more of 5% or less Mo, 5% or less Cu, 2% or less Crand 0.5% or less Mn with the rest consisting of Fe and inevitableimpurities, that has been described in conjunction with the prior artmay be used.

Therefore, the iron particles, Fe—Si based soft magnetic iron alloyparticles, Fe—Al based soft magnetic iron alloy particles, Fe—Si—Albased soft magnetic iron alloy particles, Fe—Cr based soft magnetic ironalloy particles or nickel-based soft magnetic alloy particles includedin the composite soft magnetic sintered material of the presentinvention having high density and high magnetic permeability are made ofthe soft magnetic metal particles of the same composition as that of thesoft magnetic metal powder described above, and the ferrite phase havinga spinel structure that covers the soft magnetic metal particles andseparates the particles is a ferrite phase represented by the generalformula (MeFe)₃O₄ (where Me represents Mn, Zn, Ni, Mg, Cu, Fe or Co, ora mixture of some of these elements).

The iron powder, Fe—Si based soft magnetic iron alloy powder, Fe—Albased soft magnetic iron alloy powder, Fe—Si—Al based soft magnetic ironalloy powder, Fe—Cr based soft magnetic iron alloy powder ornickel-based soft magnetic alloy powder, of which particles are coatedwith layers of ferrite having a spinel structure on the surface thereof,that are used as the feed stock powder in producing the composite softmagnetic sintered material of the present invention having high densityand high magnetic permeability can be made by forming the ferrite layerby a chemical plating process, high-speed impact agitation coatingprocess or binder coating process.

The composite soft magnetic sintered material of the present inventionhaving high density and high magnetic permeability can be produced byany of the methods (4) to (9) described above using the composite softmagnetic powder made as described above.

The compression molding process and the high-pressure molding processemployed in the methods of (4), (6) and (8) described above aredifferent only in the molding pressure. The high-pressure moldingprocess molds powder with a pressure higher than in the ordinarycompression molding process, and has the merit that the compressed bodymade by the high-pressure molding process can be sintered at a somewhatlower temperature.

The term “sintering” used in the method of producing the composite softmagnetic sintered material of the present invention having high densityand high magnetic permeability includes liquid phase sintering as wellas solid phase sintering. Therefore, sintering carried out in themethods of (4), (6) and (8) described above includes liquid phasesintering as well as solid phase sintering.

The reason for limiting the mean powder particle size of the silicondioxide powder included in the composite soft magnetic sintered materialof the present invention having high density and high magneticpermeability to 100 nm or less is that the effect of improving thesintering characteristic decreases and the relative magneticpermeability decreases when the mean powder particle size of the silicondioxide powder is larger than 100 nm. The lower limit of the mean powderparticle size of the silicon dioxide powder is preferably 1 nm or largerfor reasons of the production cost.

The reason for setting the content of the silicon dioxide powder of amean powder particle size within 100 nm to 0.05% by weight or more isthat the sintering characteristics are not significantly affected andrelative magnetic permeability decreases when less than 0.05% by weightof the silicon dioxide powder of a mean powder particle size within 100nm is included, while the content exceeding 1.0% by weight hasundesirable effects such as increasing the proportion of nonmagneticphase and decreasing the relative magnetic permeability. The content ofthe silicon dioxide powder is most preferably in a range from 0.1 to0.5% by weight.

EXAMPLE 1

An alloy material was melted by induction melting, with the resultantmolten metal being subjected to water atomization so as to make anatomized powder, and the atomized powder was classified to prepareatomized feed stock powder. The atomized feed stock powder wasclassified further with an air classifier thereby to make a softmagnetic powder such as pure iron powder, Fe—Si based soft magnetic ironalloy powder, Fe—Al based soft magnetic iron alloy powder, Fe—Si—Albased soft magnetic iron alloy powder, Fe—Cr based soft magnetic ironalloy powder and nickel-based soft magnetic alloy powder that hadcompositions and a mean powder particle sizes shown in Tables 1 and 2(hereinafter these soft magnetic powders are referred to as softmagnetic metal powder). These soft magnetic metal powders were immersedin ion exchange water, stirred well and were fully deoxidized withnitrogen.

Aqueous solutions of metal chlorides having the oxide composition shownin Tables 1 and 2 were prepared by dissolving metal chlorides (MCl₂,where M represents Fe, Ni, Zn, Cu, Mn or Mg) in ion exchange water thatbad been fully deoxidized with nitrogen. The aqueous solutions of metalchlorides were gently poured onto the soft magnetic metal powders, andthe pH value was adjusted to 7.0 by means of an aqueous solution ofNaOH. This mixed liquid was held at a constant temperature of 70° C.,and was stirred mildly while blowing air therein for a period of 0.3 to3 hours, thereby to form a ferrite coating layer on the surfaces of theparticles of the soft magnetic metal powder. Then the soft magneticmetal powder coated with ferrite layer was filtered, washed in water anddried thereby to obtain the composite soft magnetic powder.

SiO₂ powder having the mean powder particle size shown in Tables 1 and 2was mixed in the composite soft magnetic powder obtained as describedabove, with the mixture being pressed with a pressure of 6 tons/cm² tomold ring-shaped green compacts measuring 35 mm in outer diameter, 25 mmin inner diameter and 5 mm in height. The ring-shaped green compact wassintered in an inert gas atmosphere with a controlled partial pressureof oxygen at temperature from 600 to 1200° C., thereby making compositesoft magnetic sintered materials of the present invention 1 to 16,comparative composite soft magnetic sintered materials 1 to 3 andcomposite soft magnetic sintered material of the prior art, all having aring shape. SEM observation of the structures of ring-shaped sinteredbodies showed SiO₂ powder dispersed in the ferrite phase in all thecomposite soft magnetic sintered materials of the present invention 1 to16 and the comparative composite soft magnetic sintered materials 1 to3. The relative density was measured on the composite soft magneticsintered materials of the present invention 1 to 16, the comparativecomposite soft magnetic sintered materials 1 to 3 and the composite softmagnetic sintered material of the prior art, with the results shown inTables 3 and 4. The relative magnetic permeability at high frequencieswas measured at frequencies shown in Tables 3 and 4 with an impedanceanalyzer on the composite soft magnetic sintered materials of thepresent invention 1 to 16, the comparative composite soft magneticsintered materials 1 to 3 and the composite soft magnetic sinteredmaterial of the prior art, with the results shown in Tables 3 and 4.

TABLE 1 Composite soft magnetic powder Soft magnetic metal powderFerrite coating layer SiO₂ powder Composite soft Mean powder Mean Meanpowder magnetic sintered Composition particle size Composition thicknessparticle size Content (% by materials (% by weight) (μm) (atomic %) (μm)(nm) weight) Composite 1 Fe: 100 52 (Mn₃₃Fe₆₇)₃O₄ 0.2 10 0.6 softmagnetic 2 Fe: 100 78 (Mn₁₇Zn₁₆Fe₆₇)₃O₄ 1.4 30 0.8 sintered 3 Fe: 100 88(Ni₁₀Zn₁₉Fe₇₁)₃O₄ 1.2 80 0.3 materials of 4 Fe: 99, Si: 1 69(Cu₅Mg₅Zn₂₃Fe₆₇)₃O₄ 2.4 30 0.2 present 5 Fe: 97, Si: 3 90(Mn₁₆Mg₅Zn₁₄Fe₇₁)₃O₄ 0.8 80 0.9 invention 6 Fe: 90, Al: 10 76(Mn₁₀Cu₅Zn₁₈Fe₆₇)₃O₄ 1.7 30 0.15 7 Fe: 85, Si: 10, Al: 5 85(Mn₂₅Fe₇₅)₃O₄ 2.0 80 0.7 8 Fe: 51, Ni: 49 49 (Mn₁₇Zn₁₂Fe₇₁)₃O₄ 0.4 100.07 9 Fe: 21, Ni: 79 55 (Mn₁₀Cu₅Zn₁₄Fe₇₁)₃O₄ 1.9 10 0.4 10 Fe: 16, Ni:79, Mo: 5 63 (Ni₁₀Zn₂₃Fe₆₇)₃O₄ 0.5 30 0.5 11 Fe: 95, Cr: 5 48(Ni₁₀Zn₁₅Fe₇₅)₃O₄ 2.3 30 0.2

TABLE 2 Composite soft magnetic powder SiO₂ powder Soft magnetic metalpowder Mean Composite soft Mean powder Ferrite coating layer powdermagnetic sintered Composition (% by particle size Composition Meanparticle size Content (% materials weight) (μm) (atomic %) thickness(μm) (nm) by weight) Composite soft 12 Fe: 91, Cr: 9 76(Ni₁₀Cu₅Zn₁₅Fe₇₀)₃O₄ 1.7 80 0.5 magnetic 13 Fe: 87, Cr: 13 61(Mn₂₅Fe₇₅)₃O₄ 2.2 80 0.3 sintered 14 Fe: 83, Cr17 78 (Ni₅Zn₂₀Fe₇₅)₃O₄1.4 10 0.5 materials of 15 Fe: 93, Cr: 3, Al: 2 52 (Ni₁₀Cu₅Mn₁₈Fe₆₇)₃O₄0.1 30 0.1 present 16 Fe: 90, Cr: 9, Si: 1 84 (Ni₁₀Zn₂₃Fe₆₇)₃O₄ 0.7 300.8 invention Comparative 1 Fe: 100 78 (Mn₁₅Mg₅Zn₉Fe₇₁)₃O₄ 1.5 120* 0.2composite soft 2 Fe: 97, Si: 3 90 (Mn₂₉Fe₇₁)₃O₄ 0.3 30 0.02* magnetic 3Fe: 21, Ni: 79 55 (Ni₆Zn₂₃Fe₇₁)₃O₄ 0.9 30 1.2^(a) sintered materialsComposite soft Fe: 100 78 (Ni₁₀Zn₂₃Fe₆₇)₃O₄ 1.5 — — magnetic sinteredmaterial of the prior art Figures marked with * are out of the scope ofthe present invention.

TABLE 3 Composite soft magnetic Relative Relative magnetic permeabilityat various frequencies sintered materials density (%) 1 KHz 3 KHz 10 KHz30 KHz 100 KHz 300 KHz 1 MHz Composite soft 1 95 312 313 313 311 312 301232 magnetic sintered 2 94 301 299 298 300 301 299 273 materials ofpresent 3 94 291 277 279 278 277 275 251 invention 4 95 279 277 279 278277 275 251 5 93 292 291 292 292 294 265 189 6 93 288 288 289 288 289285 276 7 96 286 284 285 285 281 264 203 8 93 304 304 305 304 301 286207 9 94 290 289 290 290 289 289 280 10 94 321 321 321 320 321 319 29611 92 289 290 290 288 266 241 212

TABLE 4 Composite soft magnetic Relative Relative magnetic permeabilityat various frequencies sintered materials density (%) 1 KHz 3 KHz 10 KHz30 KHz 100 KHz 300 KHz 1 MHz Composite soft magnetic 12 95 300 299 300300 299 296 279 sintered materials of present 13 95 296 295 296 296 287262 207 invention 14 94 290 290 291 290 276 254 204 15 96 307 307 307305 305 300 292 16 94 301 300 300 300 297 291 274 Comparative compositesoft 1 90 224 224 222 223 221 206 147 magnetic sintered materials 2 89231 230 230 231 228 210 122 3 88 206 206 207 206 207 205 172 Compositesoft magnetic 85 212 211 212 212 212 210 181 sintered material of theprior art

From the results shown in Tables 1 to 4, it can be seen that thecomposite soft magnetic sintered materials of the present invention 1 to16, that were made by compression molding and sintering of the mixtureof composite soft magnetic powder consisting of soft magnetic metalpowder coated with layers of ferrite having a spinel structure on thesurface thereof and 0.05 to 1.0% by weight of SiO₂ powder, have higherdensity than the composite soft magnetic sintered material of the priorart and excellent relative magnetic permeability at high frequencies,although the comparative composite soft magnetic sintered materials of 1to 3 are inferior in at least one of density and relative magneticpermeability.

EXAMPLE 2

Molten metal was subjected to water atomization so as to make atomizedpowder, and the atomized powder was classified to prepare atomized feedstock powder. The atomized feed stock powder was classified further withan air classifier thereby to make the soft magnetic metal powders havingcompositions and the mean powder particle sizes shown in Tables 5. Thesesoft magnetic metal powders were immersed in ion exchange water, stirredwell and were fully deoxidized with nitrogen.

Aqueous solutions of metal chlorides having the oxide compositions shownin Tables 5 were prepared by dissolving metal chlorides (MCl₂, where Mrepresents Fe, Zn, Cu, Mn or Mg) in ion exchange water that had beenfully deoxidized with nitrogen. The aqueous solutions of metal chlorideswere gently poured onto the soft magnetic metal powders, with the pHvalue thereof being adjusted to 7.0 by means of an aqueous solution ofNaOH. This mixed liquid was held at a constant temperature of 70° C.,and was stirred mildly while blowing air therein for a period of 0.3 to3 hours, thereby to form a ferrite coating layer on the surfaces of theparticles of the soft magnetic metal powder. Then the soft magneticmetal powder coated with the ferrite coating layer was filtered, washedin water and dried thereby to obtain composite soft magnetic powders Ato G having ferrite coating layer formed on the particles thereof shownas in Table 5.

The composite soft magnetic powders A to G obtained as described abovewere mixed in the proportions shown in Tables 6 and 7 and were pressedwith a pressure of 6 tons/cm² to mold a ring-shaped green compactsmeasuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm inheight. The ring-shaped green compacts were sintered in an inert gasatmosphere with controlled partial pressure of oxygen at temperaturefrom 600 to 1200° C., thereby making composite soft magnetic sinteredmaterials of the present invention 17 to 30 and the composite softmagnetic sintered materials of the prior art 1 to 7, all having a ringshape. The relative density was measured on the composite soft magneticsintered materials of the present invention 17 to 30 and the compositesoft magnetic sintered materials of the prior art 1 to 7, with theresults shown in Tables 6 and 7. The relative magnetic permeability athigh frequencies was measured with an impedance analyzer at thefrequencies shown in Tables 6 and 7 on the composite soft magneticsintered materials of the present invention 17 to 30, and the compositesoft magnetic sintered material of the prior art 1 to 7, with theresults shown in Tables 6 and 7.

TABLE 5 Soft magnetic metal powder Ferrite coating layer CompositionMean powder particle Composition Mean Type (% by weight) size (μm)(atomic %) thickness (μm) Composite soft A Fe: 100 52 (Mn₃₃Fe₆₇)₃O₄ 0.2magnetic powders B Fe: 100 78 (Mn₁₇Zn₁₆Fe₆₇)₃O₄ 1.4 C Fe: 99, Si: 1 69(Cu₅Mg₅Zn₂₃Fe₆₇)₃O₄ 2.4 D Fe: 97, Si: 3 90 (Mn₁₀Mg₅Zn₁₄Fe₇₁)₃O₄ 0.8 EFe: 90, Al: 10 76 (Mn₁₀Cu₅Zn₁₈Fe₆₇)₃O₄ 1.7 F Fe: 21, Ni: 79 66(Mn₁₀Cu₅Zn₁₅Fe₇₀)₃O₄ 0.5 G Fe: 87, Cr: 13 61 (Mn₂₅Fe₇₅)₃O₄ 2.2

TABLE 6 Proportions of composite Composite soft magnetic powders shownRelative Relative magnetic permeability soft magnetic in Table 5 (% byweight) density at various frequencies sintered materials A B C D E F G(%) 1 KHz 3 KHz 10 KHz 30 KHz 100 KHz 300 KHz 1 MHz Composite soft 19 50— 50 — — — — 96 286 286 287 286 287 281 255 magnetic sintered 20 — 70 —— 30 — — 94 293 292 293 293 293 276 234 materials of 21 — — 40 60 — — —94 288 286 286 287 286 270 217 present invention 22 40 — — 30 30 — — 95305 305 305 304 305 294 264 23 — 80 10 10 — — — 93 307 306 306 307 306300 266 24 20 20 — — 60 — — 94 278 278 279 279 278 272 259 25 30 — 20 3020 — — 93 291 290 290 290 290 276 251 26 — 20 20 30 30 — — 93 287 288287 287 288 273 254 27 10 50 10 10 20 — — 96 302 302 303 302 302 282 26728 20 10 20 30 10 — — 95 294 295 294 295 295 291 269 29 40 — — — — 60 —96 293 291 292 291 290 272 244 30 — 20 30 — — — 50 94 290 290 291 290287 271 237 31 20 — — 10 20 20 30 93 298 298 297 298 297 287 268 32 1020 10 10 20 20 10 94 301 303 303 302 300 284 270

TABLE 7 Proportion of composite soft magnetic Composite soft powdersshown in Table 5 Relative Relative magnetic permeability magneticsintered (% by weight) density at various frequencies materials A B C DE F G (%) 1 KHz 3 KHz 10 KHz 30 KHz 100 KHz 300 KHz 1 MHz Composite 1100 — — — — — — 88 230 230 229 230 216 298 106 soft 2 — 100 — — — — — 89225 225 225 222 204 161 95 magnetic 3 — — 100 — — — — 89 212 211 211 211212 204 143 sintered 4 — — — 100 — — — 90 219 218 218 217 218 202 135materials 5 — — — — 100 — — 89 227 227 226 227 226 211 174 of the 6 — —— — — 100 — 87 222 223 223 222 218 203 181 prior art 7 — — — — — — 10089 206 206 205 205 198 195 149

From the results shown in Tables 5 to 7, it can be seen that thecomposite soft magnetic sintered materials of the present invention 17to 30, that were made by mixing and sintering the composite softmagnetic powders consisting of the soft magnetic metal powders coatedwith ferrite coating layers of a different composition and having aspinel structure on the surface thereof, have higher density than thecomposite soft magnetic sintered material of the prior art 1 to 7 andexcellent relative magnetic permeability at high frequencies.

EXAMPLE 3

The composite soft magnetic powders A to G made in Example 2 were mixedfurther with SiO₂ powder in the proportions shown in Table 8 and werepressed with pressure of 6 tons/cm² to mold a ring-shaped green compactsmeasuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm inheight. The ring-shaped green compacts were sintered in an inert gasatmosphere with a controlled partial pressure of oxygen at a temperaturefrom 600 to 1200° C., thereby making the composite soft magneticsintered materials of the present invention 31 to 36. The relativedensity was measured on the composite soft magnetic sintered materialsof the present invention 31 to 36, with the results shown in Table 8.The relative magnetic permeability at high frequencies was measured withan impedance analyzer at the frequencies shown in Table 8 on thecomposite soft magnetic sintered materials of the present invention 31to 36, with the results shown in Table 8.

TABLE 8 Proportion (% by weight) SiO₂ powder of mean Composite powderRela- soft Composite soft particle tive magnetic magnetic powder sizeden- Relative magnetic permeability sintered shown in Table 5 shown sityat various frequencies materials A B C C E F G in ( ) (%) 1 KHz 3 KHz 10KHz 30 KHz 100 KHz 300 KHz 1 MHz Composite 31 — 40   — — 20 39.6 — 0.497 304 305 304 305 305 292 254 soft (30 nm) magnetic 32 29.1 — — 20 20 —30   0.9 97 308 309 309 308 308 305 296 sintered (80 nm) materials 3310   10   20   — — 30 29.1 0.1 96 299 299 298 298 295 278 244 of (10 nm)present 34 40   — — 20 — 39.4 — 0.6 96 302 302 300 301 300 292 277invention (10 nm) 35 — 59.5 — — — 40 — 0.5 98 316 314 314 315 313 303291 (30 nm) 36 — — 39.3 — 20 — 40   0.7 96 302 302 303 302 302 300 286(80 nm)

It can be seen that the composite soft magnetic sintered materials ofthe present invention 31 to 36 shown in Table 8, that were made bymixing the composite soft magnetic powders consisting of the softmagnetic metal powder coated with the ferrite coating layer having aspinel structure and a different composition on the surfaces of theparticles thereof with SiO₂ powder in the proportions shown in Table 8and sintering the mixture, have higher density than the composite softmagnetic sintered material of the prior art 1 to 7 shown in Table 7 thatwere made in Example 2 and excellent relative magnetic permeability athigh frequencies.

EXAMPLE 4

The soft magnetic metal powder shown in Table 9 and ferrite powder weremixed in proportions of soft magnetic metal powder: ferrite powder=98:2.The mixed powder was processed for two minutes in a high-speed impactmixer with an impeller rotating at a speed of 6000 rpm, thereby makingthe composite soft magnetic powders AS, BS, CS, DS, ES, FS and GS havinga ferrite coating layer on the particles thereof shown in Table 9.

A SiO₂ powder having a mean powder particle size of 50 nm was mixed withthe composite soft magnetic powders AB, BB, CB, DB, EB, FB and GBobtained as described above in the proportions shown in Table 14, withthe mixted power being subjected to high-pressure of 2 tons/cm2 at 8000Cso as to mold the composite soft magnetic sintered materials of thepresent invention 37 to 43 having a ring shape measuring 35 mm in outerdiameter, 25 mm in inner diameter and 5 mm in height. TEM Auger electronspectrometer (AES) observation of the structures of ring-shaped sinteredbodies showed 5i02 powder dispersed in the ferrite phase in all thecomposite soft magnetic sintered materials of the present invention 37to 43. The relative density was measured on the composite soft magneticsintered materials of the present invention 37 to 43, with the resultsshown in Table 10. The relative magnetic permeability at highfrequencies was measured with an impedance analyzer at the frequenciesshown in Table 10 on the composite soft magnetic sintered materials ofthe present invention 37 to 43, with the results shown in Table 10.

TABLE 9 Soft magnetic metal powder Ferrite coating layer CompositionMean powder particle Mean Type (% by weight) size (μm) Composition(atomic %) thickness (μm) Composite AS Fe: 100 52 (Mn₃₃Fe₆₇)₃O₄ 1.7 softBS Fe: 100 78 (Mn₁₇Zn₁₆Fe₆₇)₃O₄ 1.5 magnetic CS Fe: 99, Si: 1 69(Cu₅Mg₅Zn₂₃Fe₆₇)₃O₄ 2.1 sintered DS Fe: 97, Si: 3 90(Mn₁₀Mg₅Zn₁₄Fe₇₁)₃O₄ 1.9 materials ES Fe: 90, Al: 10 76(Mn₁₀Cu₅Zn₁₈Fe₆₇)₃O₄ 2.4 FS Fe: 21, Ni: 79 66 (Mn₁₀Cu₅Zn₁₅Fe₇₀)₃O₄ 2.0GS Fe: 87, Cr: 13 61 (Mn₂₅Fe₇₅)₃O₄ 1.2

TABLE 10 Proportion (% by weight) Composite soft Composite SiO₂ powderRelative Relative magnetic permeability magnetic sintered soft magneticpowder having mean powder density at various frequencies materials shownin Table 9 particle size of 50 nm (%) 1 KHz 3 KHz 10 KHz 30 KHz 100 KHz300 KHz 1 MHz Composite 37 AS: 99.6 0.4 93 310 311 310 310 309 288 221soft magnetic 38 BS: 99.1 0.9 92 275 276 276 277 276 274 209 sintered 39CS: 99.9 0.1 94 308 308 309 309 308 286 222 materials of 40 DS: 99.4 0.693 298 299 298 297 297 280 215 present 41 ES: 99.5 0.5 93 299 299 299298 297 278 210 invention 42 FS: 99.3 0.7 92 285 286 285 286 285 272 20343 GS: 99.7 0.3 94 291 292 292 291 291 283 218

From the results shown in Tables 9 and 10, it can be seen that thecomposite soft magnetic sintered materials of the present invention 37to 43, that were made by mixing 0.05 to 1.0% by weight of SiO₂ powderwith the composite soft magnetic powders AS, BS, CS, DS, ES, FS and GSconsisting of the soft magnetic metal powder of which particles arecoated with a ferrite layer having a spinel structure by a high-speedimpact stirring coating method and processing the mixture by a hotpressing process, have higher density than the composite soft magneticsintered material of the prior art 1 to 7 shown in Table 7 and excellentrelative magnetic permeability at high frequencies.

EXAMPLE 5

The composite soft magnetic powders AS, BS, CS, DS, ES, FS and GS shownin Table 9 made in Example 4 were mixed in the proportions shown inTable 11. The mixed powders were hot-pressed with a pressure of 2tons/cm² at 800° C. so as to make the composite soft magnetic sinteredmaterials of the present invention 44 to 53 having a ring shapemeasuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm inheight. The relative density was measured on the composite soft magneticsintered materials of the present invention 44 to 53, with the resultsshown in Table 11. The relative magnetic permeability at highfrequencies was measured with an impedance analyzer at the frequenciesshown in Table 11 on the composite soft magnetic sintered materials ofthe present invention 44 to 53, with the results shown in Table 11.

TABLE 11 Proportion of composite Composite soft magnetic powder RelativeRelative magnetic permeability soft magnetic shown in Table 9 (% byweight) density at various frequencies sintered materials AS BS CS DS ESFS GS (%) 1 KHz 3 KHz 10 KHz 30 KHz 100 KHz 300 KHz 1 MHz Composite soft44 50 — 50 — — — — 95 295 296 295 295 295 282 253 magnetic sintered 45 —70 — — 30 — — 96 299 301 300 300 300 290 260 materials of 46 — — 40 60 —— — 96 296 296 295 296 296 284 257 present invention 47 40 — — 30 — — 3093 286 286 285 285 284 265 235 48 — 80 10 10 — — — 94 293 293 293 292293 276 256 49 — 20 — — 60 20 — 95 303 303 302 302 303 294 268 50 30 —20 30 20 — — 96 297 299 298 299 298 293 266 51 — 20 20 30 30 — — 95 291290 290 291 290 287 260 52 10 — 10 10 20 — 50 94 290 290 290 289 288 280252 53 20 10 20 — 10 30 — 95 301 302 301 302 300 298 271

From the results shown in Table 11, it can be seen that the compositesoft magnetic sintered materials of the present invention 44 to 53, thatwere made by mixing the composite soft magnetic powders consisting ofthe soft magnetic metal powders of which particles are coated withferrite layer of a different composition having a spinel structure andsintering the mixed powder, have higher density than the composite softmagnetic sintered materials of the prior art 1 to 7 shown in Table 7 andexcellent relative magnetic permeability at high frequencies.

EXAMPLE 6

Two or more kinds of the composite soft magnetic powders AS to GS shownin table 9 made in Example 4 were mixed and the mixture was furthermixed with SiO₂ powder having a mean powder particle size of 50 nm inthe proportions shown in Table 12. The mixtures were hot-pressed with apressure of 2 tons/cm² at 800° C. so as to make composite soft magneticsintered materials of the present invention 54 to 59 having a ring shapemeasuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm inheight. The relative density was measured on the composite soft magneticsintered materials of the present invention 54 to 59, with the resultsshown in Table 12. The relative magnetic permeability at highfrequencies was measured with an impedance analyzer at the frequenciesshown in Table 12 on the composite soft magnetic sintered materials ofthe present invention 54 to 59, with the results shown in Table 12.

TABLE 12 Composite Proportion Rela- soft (% by weight) tive magneticComposite soft magnetic den- Relative magnetic permeability sinteredpowder shown in Table 9 SiO₂ sity at various frequencies materials AS BSCS DS ES FS GS powder (%) 1 KHz 3 KHz 10 KHz 30 KHz 100 KHz 300 KHz 1MHz Composite 54 — 40   — — 20 39.6 — 0.4 96 302 303 303 303 303 292 250soft 55 29.1 — — 20 20 — 30   0.9 97 307 307 308 308 307 304 293magnetic 56 10   10   20   — — 30   29.1 0.1 96 299 299 300 300 299 270238 sintered 57 40   — — 20 — 39.4 — 0.6 97 305 305 304 304 303 300 282materials 58 — 59.5 — — — 40   — 0.5 98 309 310 310 309 309 305 288 ofpresent 59 — — 39.3 — 20 — 40   0.7 97 300 301 300 299 299 298 280invention

It can be seen that the composite soft magnetic sintered materials ofthe present invention 54 to 59 shown in Table 12, that were made bymixing the composite soft magnetic powders consisting of the softmagnetic metal powder of which particles were coated with ferrite layerhaving a spinel structure of a different composition with SiO₂ powder inthe proportions shown in Table 12 and sintering the mixed powder, have ahigher density than the composite soft magnetic sintered material of theprior art 1 to 7 shown in Table 7 that were made in Example 2 andexcellent relative magnetic permeability at high frequencies.

EXAMPLE 7

The soft magnetic metal powders having the compositions shown in Table13 were charged into a rolling agitation granulating apparatus to which200 ml of polyvinyl alcohol solution 3% in concentration and ferritepowder in a proportion of 2% by weight to the soft magnetic metal powderwere added so as to mix for 30 minutes while running the apparatus at aspeed of 1000 rpm, thereby making composite soft magnetic powders AB,BB, CB, DB, EB, FB and GB shown in Table 13 by a binder coating process.

A SiO₂ powder having a mean powder particle size of 50 nm was mixed withthe composite soft magnetic powders AB, BB, CB, DB, EB, FB and GBobtained as described above in the proportions shown in Table 14, withthe mixed powder being subjected to high-pressure molding with apressure of 10 tons/cm2 so as to mold ring-shaped green compactsmeasuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm inheight. The ring-shaped green compacts were sintered at a temperaturefrom 500 to 1200° C., thereby making the composite soft magneticsintered materials of the present invention 60 to 66 having a ringshape. Auger electron spectrometer (AES) observation of the structuresof the ring-shaped sintered bodies thus obtained showed 5i02 powderdispersed in the ferrite phase in all the composite soft magneticsintered materials of the present invention 60 to 66. Results ofanalysis of the SiO₂ included in the grain boundary of the compositesoft magnetic sintered material 61, in particular, with a surfaceanalysis apparatus (Auger electron analyzer (AES), product name PhysicalElectronics 670xi produced by Perkin Elmer) are shown in FIGS. 1 and 2.FIG. 1 is a secondary electron image of the grain boundary and FIG. 2 isAuger electron image of Si in the grain boundary, which shows thedistribution of SiO₂. From FIGS. 1 and 2, it can be seen that SiO₂ isdispersed substantially uniformly in the ferrite phase in the grainboundary. The relative density was measured on the composite softmagnetic sintered materials of the present invention 60 to 66, with theresults shown in Table 14. The relative magnetic permeability at highfrequencies was measured with an impedance analyzer at the frequenciesshown in Table 14 on the composite soft magnetic sintered materials ofthe present invention 60 to 66, with the results shown in Table 14.

TABLE 13 Soft magnetic metal powder Ferrite coating layer CompositionMean powder Composition Mean Type (% by weight) particle size (μm)(atomic %) thickness (μm) Composite soft AB Fe: 100 52 (Mn₃₃Fe₆₇)₃O₄ 2.1magnetic BB Fe: 100 78 (Mn₁₇Zn₁₆Fe₆₇)₃O₄ 2.8 sintered CB Fe: 99, Si: 169 (Cu₃Mg₃Zn₂₃Fe₆₇)₃O₄ 1.4 materials DB Fe: 97, Si: 3 90(Mn₁₀Mg₅Zn₁₄Fe₇₁)₃O₄ 2.0 EB Fe: 90, Al: 10 76 (Mn₁₀Cu₅Zn₁₈Fe₆₇)₃O₄ 2.9FB Fe: 21, Ni: 79 66 (Mn₁₀Cu₅Zn₁₅Fe₇₀)₃O₄ 2.8 GB Fe: 87, Cr: 13 61(Mn₂₅Fe₇₅)₃O₄ 1.4

TABLE 14 Proportion (% by weight) Composite soft Composite soft SiO₂powder having Relative Relative magnetic permeability magnetic sinteredmagnetic powder mean powder particle density at various frequenciesmaterials shown in Table 13 size of 50 nm (%) 1 KHz 3 KHz 10 KHz 30 KHz100 KHz 300 KHz 1 MHz Composite soft 60 AB: 99.6 0.4 93 309 310 310 309309 287 223 magnetic 61 BB: 99.1 0.9 92 276 276 275 276 276 273 210sintered 62 CB: 99.9 0.1 94 305 306 305 306 304 300 218 materials of 63DB: 99.4 0.6 92 290 290 289 288 288 279 213 present 64 EB: 99.5 0.5 92289 290 291 290 289 277 208 invention 65 FB: 99.3 0.7 91 275 274 275 274273 255 212 66 GB: 99.7 0.3 93 301 301 300 300 300 280 211

From the results shown in Tables 13 and 14, it can be seen that thecomposite soft magnetic sintered materials of the present invention 60to 66, that were made by mixing 0.05 to 1.0% by weight of SiO₂ powderwith the composite soft magnetic powders AB, BB, CB, DB, EB, FB and GBconsisting of the soft magnetic metal powders of which particles werecoated with ferrite layer having a spinel structure by a binder coatingmethod and hot pressing the mixed powder, have a higher density than thecomposite soft magnetic sintered material of the prior art 1 to 7 shownin Table 7 and excellent relative magnetic permeability at highfrequencies.

EXAMPLE 8

The composite soft magnetic powders AB, BB, CB, DB, EB, FB and GB shownin Table 13 made in Example 7 were mixed in proportions shown in Table15. The mixed powders were subjected to high-pressure molding with apressure of 10 tons/cm² so as to make composite soft magnetic sinteredmaterials of the present invention 67 to 76 having a ring shapemeasuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm inheight. The relative density was measured on the composite soft magneticsintered materials of the present invention 67 to 76, with the resultsshown in Table 15. The relative magnetic permeability at highfrequencies was measured with an impedance analyzer at frequencies shownin Table 15 on the composite soft magnetic sintered materials of thepresent invention 67 to 76, with the results shown in Table 15.

TABLE 15 Proportion of composite soft Composite magnetic powder shown inRelative Relative magnetic permeability soft magnetic Table 13 (% byweight) density at various frequencies sintered materials AB BB CB DB EBFB GB (%) 1 KHz 3 KHz 10 KHz 30 KHz 100 KHz 300 KHz 1 MHz Composite soft67 50 — 50 — — — — 95 293 294 293 294 293 285 261 magnetic sintered 68 —70 — — 30 — — 95 290 290 291 290 290 278 262 materials of 69 — — 40 60 —— — 96 295 295 294 295 294 284 260 present invention 70 40 — — 30 — — 3094 281 282 282 281 280 261 240 71 — 80 10 10 — — — 94 290 290 289 289287 276 257 72 — 20 — — 60 20 — 95 300 301 301 300 299 295 268 73 30 —20 30 20 — — 95 291 290 290 290 290 292 257 74 — 20 20 30 30 — — 94 286285 286 285 285 280 255 75 10 — 10 10 20 — 50 94 288 288 289 288 287 275254 76 20 10 20 — 10 30 — 96 300 302 301 300 301 297 270

From the results shown in Tables 15, it can be seen that the compositesoft magnetic sintered materials of the present invention 67 to 76, thatwere made by mixing the composite soft magnetic powders consisting ofthe soft magnetic metal powders of which particles were coated withlayers of ferrite having a spinel structure of a different compositionand sintering the mixed powder, have higher density than the compositesoft magnetic sintered material of the prior art 1 to 7 shown in Table7, and excellent relative magnetic permeability at high frequencies.

EXAMPLE 9

Two or more kinds of the composite soft magnetic powders AB to GB shownin Table 13 made in Example 7 were mixed and the mixture was furthermixed with SiO₂ powder having a mean powder particle size of 50 nm inproportion shown in Table 16. The mixed powder was hot-pressed with apressure of 2 tons/cm² at 800° C. so as to make composite soft magneticsintered materials of the present invention 77 to 82 having a ring shapemeasuring 35 mm in outer diameter, 25 mm in inner diameter and 5 mm inheight. The relative density was measured on the composite soft magneticsintered materials of the present invention 77 to 82, with the resultsshown in Table 16. The relative magnetic permeability at highfrequencies was measured with an impedance analyzer at frequencies shownin Table 16 on the composite soft magnetic sintered materials of thepresent invention 77 to 82, with the results shown in Table 16.

TABLE 16 Composite Rela- soft Proportion (% by weight) tive magneticComposite soft magnetic den- Relative magnetic permeability sinteredpowder shown in Table 13 SiO₂ sity at various frequencies materials ABBB CB DB EB FB GB powder (%) 1 KHz 3 KHz 10 KHz 30 KHz 100 KHz 300 KHz 1MHz Composite 77 — 40   — — 20 39.6 — 0.4 96 300 300 301 299 299 291 251soft 78 29.1 — — 20 20 — 30   0.9 97 304 304 303 304 304 300 290magnetic 79 10   10   20   — — 30   29.1 0.1 97 298 299 299 298 297 272240 sintered 80 40   — — 20 — 39.4 — 0.6 96 301 301 300 300 300 291 273materials 81 — 59.5 — — — 40   — 0.5 97 299 300 300 300 299 294 278 ofpresent 82 — — 39.3 — 20 — 40   0.7 96 297 297 297 296 295 290 270invention

It can be seen that the composite soft magnetic sintered materials ofthe present invention 77 to 82, that were made by mixing the compositesoft magnetic powders consisting of the soft magnetic metal powder ofwhich particles were coated with ferrite layer having a spinel structureof a different composition with SiO₂ powder in proportion shown in Table16 and sintering the mixed powder, have a higher density than thecomposite soft magnetic sintered material of the prior art 1 to 7 shownin Table 7 that were made in Example 2 and excellent relative magneticpermeability at high frequencies.

As will be understood from the foregoing detailed description, thepresent invention provides the composite soft magnetic sintered materialhaving high industrial applicability, offering remarkable effects in theelectrical and electronics industries.

1. A composite soft magnetic sintered material having high density andhigh magnetic permeability, the sintered material comprising particlescoated with a ferrite phase that has a spinel structure, wherein theparticles are selected from the group consisting of iron particles,Fe—Si based soft magnetic iron alloy particles, Fe—Al based softmagnetic iron alloy particles, Fe—Si—Al based soft magnetic iron alloyparticles, Fe—Cr based soft magnetic iron alloy particles andnickel-based soft magnetic alloy particles; silicon dioxide particleshaving a mean powder particle size of 100 nm or less are dispersed inthe ferrite phase; and, the content of silicon dioxide in the sinteredmaterial is from 0.05 to 1.0% by weight.
 2. A composite soft magneticsintered material having high density and high magnetic permeability,the sintered material comprising a mixture of first coated particles andsecond coated particles, wherein the first coated particles comprisefirst magnetic particles coated with a first ferrite phase that has aspinel structure; the second coated particles comprise second magneticparticles coated with a second ferrite phase that has a spinelstructure; the first ferrite phase and the second ferrite phase havedifferent compositions; and the first magnetic particles and the secondmagnetic particles are independently selected from the group consistingof iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Albased soft magnetic iron alloy particles, Fe—Si—Al based soft magneticiron alloy particles, Fe—Cr based soft magnetic iron alloy particles andnickel-based soft magnetic alloy particles.
 3. A composite soft magneticsintered material having high density and high magnetic permeability,the sintered material comprising a mixture of first coated particles andsecond coated particles, wherein the first coated particles comprisefirst magnetic particles coated with a first ferrite phase that has aspinel structure; the second coated particles comprise second magneticparticles coated with a second ferrite phase that has a spinelstructure; the first ferrite phase and the second ferrite phase havedifferent compositions; the first magnetic particles and the secondmagnetic particles are independently selected from the group consistingof iron particles, Fe—Si based soft magnetic iron alloy particles, Fe—Albased soft magnetic iron alloy particles, Fe—Si—Al based soft magneticiron alloy particles, Fe—Cr based soft magnetic iron alloy particles andnickel-based soft magnetic alloy particles; silicon dioxide particleshaving a mean powder particle size of 100 nm or less are dispersed amongeach of the first ferrite phase and the second ferrite phase; and thecontent of silicon dioxide in the sintered material is from 0.05 to 1.0%by weight.
 4. A method of producing a composite soft magnetic sinteredmaterial having high density and high magnetic permeability, the methodcomprising mixing a composite soft magnetic powder, which is made byforming a ferrite layer that has a spinel structure on the surfaces ofparticles of iron powder, Fe—Si based soft magnetic iron alloy powder,Fe—Al based soft magnetic iron alloy powder, Fe—Si—Al based softmagnetic iron alloy powder, Fe—Cr based soft magnetic iron alloy powderor nickel-based soft magnetic alloy powder, with 0.05 to 1.0% by weightof silicon dioxide powder having a mean powder particle size in a rangefrom 1 to 100 nm; sintering the mixed powder after compression molding,high-pressure molding, warm compaction or cold isostatic pressing; andproducing the sintered material of claim
 1. 5. A method of producing acomposite soft magnetic sintered material having high density and highmagnetic permeability, the method comprising mixing a composite softmagnetic powder, which is made by forming a ferrite layer that has aspinel structure on the surfaces of particles of iron powder, Fe—Sibased soft magnetic iron alloy powder, Fe—Al based soft magnetic ironalloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Crbased soft magnetic iron alloy powder or nickel-based soft magneticalloy powder, with 0.05 to 1.0% by weight of silicon dioxide powderhaving a mean powder particle size in a range from 1 to 100 nm;subjecting the mixed powder to hot isostatic pressing or hot pressing;and producing the sintered material of claim
 1. 6. A method of producinga composite soft magnetic sintered material having high density and highmagnetic permeability, the method comprising preparing two or more kindsof composite soft magnetic powders, which are made by forming a ferritelayer that has a spinel structure on the surfaces of particles of ironpowder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based softmagnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloypowder, Fe—Cr based soft magnetic iron alloy powder or nickel-based softmagnetic alloy powder, where the ferrite layer has a differentcomposition in each of the two or more kinds of composite soft magneticpowders; mixing and sintering the two or more kinds of composite softmagnetic powders after compression molding, high-pressure molding, warmcompaction or cold isostatic pressing; and producing the sinteredmaterial of claim
 2. 7. A method of producing a composite soft magneticsintered material having high density and high magnetic permeability,the method comprising preparing two or more kinds of composite softmagnetic powders, which are made by forming a ferrite layer that has aspinel structure on the surfaces of particles of iron powder, Fe—Sibased soft magnetic iron alloy powder, Fe—Al based soft magnetic ironalloy powder, Fe—Si—Al based soft magnetic iron alloy powder, Fe—Crbased soft magnetic iron alloy powder or nickel-based soft magneticalloy powder, where the ferrite layer has a different composition ineach of the two or more kinds of composite soft magnetic powders; mixingthe two or more kinds of composite soft magnetic powders; subjecting themixed powders to hot isostatic pressing or hot pressing; and producingthe sintered material of claim
 2. 8. A method of producing a compositesoft magnetic sintered material having high density and high magneticpermeability, the method comprising preparing two or more kinds ofcomposite soft magnetic powders, which are made by forming a ferritelayer that has a spinel structure on the surfaces of particles of ironpowder, Fe—Si based soft magnetic iron alloy powder, Fe—Al based softmagnetic iron alloy powder, Fe—Si—Al based soft magnetic iron alloypowder, Fe—Cr based soft magnetic iron alloy powder or nickel-based softmagnetic alloy powder, where the ferrite layer has a differentcomposition in each of the two or more kinds of composite soft magneticpowder; mixing two or more kinds of composite soft magnetic powders with0.05 to 1.0% by weight of silicon dioxide powder having a mean powderparticle size in a range from 1 to 100 nm sintering the mixed powdersafter compression molding, high-pressure molding, warm compaction orcold isostatic pressing; and producing the sintered material of claim 3.9. A method of producing a composite soft magnetic sintered materialhaving high density and high magnetic permeability, the methodcomprising preparing two or more kinds of composite soft magneticpowders, which are made by forming a ferrite layer that has a spinelstructure on the surfaces of particles of iron powder, Fe—Si based softmagnetic iron alloy powder, Fe—Al based soft magnetic iron alloy powder,Fe—Si—Al based soft magnetic iron alloy powder, Fe—Cr based softmagnetic iron alloy powder or nickel-based soft magnetic alloy powder,where the ferrite layer has a different composition in each of the twoor more kinds of composite soft magnetic powders; mixing the two or morekinds of composite soft magnetic powders with 0.05 to 1.0% by weight ofsilicon dioxide powder having a mean powder particle size in a rangefrom 1 to 100 nm and; subjecting the mixed powders to hot isostaticpressing or hot pressing; and producing the sintered material of claim3.
 10. The method of claim 4, wherein the ferrite layer is formed by achemical plating process, a high-speed impact agitation coating processor a binder coating process.
 11. The method of claim 5, wherein theferrite layer is formed by a chemical plating process, a high-speedimpact agitation coating process or a binder coating process.
 12. Themethod of claim 6, wherein the ferrite layer is formed by a chemicalplating process, a high-speed impact agitation coating process or abinder coating process.
 13. The method of claim 7, wherein the ferritelayer is formed by a chemical plating process, a high-speed impactagitation coating process or a binder coating process.
 14. The method ofclaim 8, wherein the ferrite layer is formed by a chemical platingprocess, a high-speed impact agitation coating process or a bindercoating process.
 15. The method of claim 9, wherein the ferrite layer isformed by a chemical plating process, a high-speed impact agitationcoating process or a binder coating process.